Field of the Invention
The present invention generally relates to a heat radiating plate and a method for producing the same. More specifically, the invention relates to a heat radiating plate integrated with radiating fins, and a method for producing the same.
Description of the Prior Art
In a conventional metal/ceramic bonding substrate used as an insulating substrate for power modules, a metal circuit plate is bonded to one side of a ceramic substrate, and a metal base plate for heat radiation is bonded to the other side thereof, the metal circuit plate mounting thereon semiconductor chips and so forth.
In order to radiate heat from heating elements, such as semiconductor chips, to the outside, there is known a method for mounting radiating fins on the reverse of a metal base plate for heat radiation via radiating grease. There is also known a method for bonding radiating fins to a semiconductor device mounting substrate via a brazing filler metal (see, e.g., Japanese Patent Laid-Open No. 4-363052).
In order to further improve the cooling power of a metal/ceramic bonding substrate, there is proposed a heat radiator which has a member integrated with a large number of columnar (or pillar) protruding portions (as radiating fins), each of which has a shape of substantially circular truncated cone (see, e.g., Japanese Patent Laid-Open No. 2007-294891).
When a large number of columnar protruding portions having a shape of substantially circular truncated cone are formed as radiating fins like a heat radiator disclosed in Japanese Patent Laid-Open No. 2007-294891, if the protruding portions are formed by a method (so-called molten metal bonding method) for cooling and solidifying a molten metal (of aluminum, an aluminum alloy or the like) injected into a mold, a great thermal stress is produced during the cooling and solidifying of the molten metal by the great difference between the thermal expansion coefficient of the mold (of isotropic carbon or the like) and that of aluminum, the aluminum alloy or the like, so that it is very difficult to release the protruding portions from the mold if a large number of radiating fins having a small tapered angle (of not greater than 5°) are formed to increase the total surface area of the radiating fins. For that reason, there are problems in that it is not possible to obtain radiating fins having a desired shape due to the flaws and breaks thereof and/or that the mold is broken.